Process of purifying alkali-metal cyanide solutions containing sulphides



Patented June 21-, 1927.

UNITED STATES PATENT OFFICE.

KURT HERRDEGEN, or,LUDwIGsmnN-oN-rnn-Rnmn, GERMANY, assienoa To I. e.FARBENINDUSTRIE .AKTIENGESELLSCHAFT, or rRaNxroRr-on-mzn-mm, GERMANY, ACORPORATION or GERMANY.

PROCESS OF PURIFYING ALKALI-METAL CYANIIDE SOLUTIONS CONTAINING SUI:-

PEDES- No Drawing. Application filed November 27, 1926, Serial No,151,268, and in Germany December 4, 1925.

, Leaving out of consideration com licated processes which are notpracticable, t e elimination of hydrogen sulphide or sulphides fromsolutions of alkali metal cyanides is possible by the action of finelydivided metallic copper ,or zinc. During the action of these metals,however, on concentrated alka'li metal cyanide solutions containingsulphides, ammonia is formed after a short time, the cyanides undergoingdecomposition. It is also found that alkali metal sul hide is stillpresent in. the solutions even a ter prolonged action of the saidmetals.

Zinc or copper hydroxid may be employed with more advantage instead ofthe metals for precipitating the combined sulphur, and lead hydroxidalso precipitates the sulphur completely and immediately in the form oflead sulphide. In this case, how- 2 ever, secondar reactions occur,insoluble metallic cyani es and soluble complex cyanides being formed,and, in the case of some hydroxids as those of lead or zinc, alkalimetal plumbite or alkali metal zincate are produced.

I have now found that combined sulphur can be immediately and completelyseparated from solutions of alkali metal cyanides, without theoccurrence of any disturbin'g secondary reactions, .by employing bismuthcompounds capable of forming bismuth sulphide such as the hydroxid orsalts of bismuth for that purpose. In this case, pure bismuth sulphideis precipitated, the re: generation of which causes no inconvenience.

The following example further illustrates how the invention may becarried out in practice but the invention is not restricted V thereto.

Example.

A cold cyanide solution, such as is obtained by leaching the crudecyanide obtained from carbon, soda ash and nitrogen by the Bucherprocess, which solution contains about per cent of sodium cyanide,

0.02 per cent of sodium sulphide and 1.0 per cent of sodium hydroxid, istreated with moist bismuth hydroxid, added slowly while stirring untilthe precipitant is in slight exn testimony whereof I have hereunto set Imy hand. KURT HERRDEGEN.

